Method of making plastic products



Patented Apr. 29, 1941 DIETHOD OF MAKING PLASTIC PRODUCTS Carlisle K. Boos, Wheaton, Delbert F. Jurgensen, Jr., Chicago, and Thomas P. Camp, Glen Ellyn, Ill., minors to United States Gypsum Com- I pany, Chicago, 111., a corporation of Illinois No Drawing. Application April 28, 1937, Serial No. 139,452

. 4 Claims.

The present invention relates to an improved form of pressed gypsum products and the methods used for their production.

One of the objects of the present invention is to produce dense, strong, and tough gypsum products from a mixture of calcined gypsum and water, with or without added'fllling materials and s'1ch strengthening agents as fiber, wood fiber, comminuted paper, and the like, which products have been rendered dense, strong, and tough by the application of pressure thereto during their formation.

A further object of the invention is a process for the production of dense,.strong, and tough gypsum products which comprises mixing calcinedgypsum with water to form a plastic mixture and thereupon confining the said mixture between absorbent sheets of fabric and compressing the same, thereby expelling some of the excess water above'that required for the setting of the gypsum into the fabric sheets and hence out of the plastic mass. These sheets may be allowed to remain in contact with the surface or surfaces of the pressed product, eventually becoming an integral part thereof as a result of the setting and drying of the gypsum core.

A further object of the invention is a process for the pressing of still unset plastic mixtures of calcined gypsum or the like containing the neces- 'sary water for the hydration and setting of the gypsum, this pressing being accomplished under conditions which are conducive to the removal of some of the excess water.

Still a further object of the invention is to produce strong, dense and tough compressed set gypsum products from plastic masses of calcined gypsum and water, with or without the addition of fibers or other strengtheningagents, in whichprocess some of the water exceeding that required for hydration is removed by pressure applied from two sides at least of the plastic material and through fibrous or other fabric sheets which define the limits of the plastic material and form an outer protective coating therefor.

Other objects of the invention will become apa flowable slurry. It has usually been found necessary to.supply more water than is theoretically required to combine with the calcined gypsum, for otherwise the plastic mass would be too dry to permit of its being shaped, or else, in the case of casting, the material would not be sufiiciently fluid to flow into molds. The strength of the resultant product is therefore considerably diminished because of the fact that when the excess water eventually escapes by evaporation, as when the product is dried, there will remain in the gypsum product innumerable interstices which naturally diminish the structural strength of the material.

. these to some extent increase the strength of the product because they act as a bonding agent which resists shattering, yet the overall strength of the material is diminished rather than enhanced by such admixture. 0n the contrary, as proposed in thepresent specification and in accordance with the present invention, a mixture of calcined gypsum, water and fibrous materials of various types is subjected to pressure sufficient to cause removal from the mixture of some of the excess water which has been mixed therewith to allow its initial shaping. The final product thus obtained will be dense, tough and strong,

, and far superiorin this respect to products which parent from the hereunto appended claims and the further description hereinbelow.

It is well known that calcium sulfate hemihydrate or other forms of calcined gypsum will unite with water to form calcium sulfate dihy- The density and strength of this mass, however, is somewhat dependent upon the amount of wa- ;-,ter which was originally mixed with the calcined gypsum to form either a plastic mass or have been allowed to set without the use of the present invention.

In its simplest form, the present invention can be carried into effect by making a mixture of calcined gypsum, water, and from 1%. to 20% or more of fiber. This fiber may be finely divided wood fiber such as may be obtained by the grinding of old newspapers, wood pulp, and the like, or may be finely comminuted sawdust or fibrated wood. ably made in such proportions as constitute a plastic material, is provided on one or more sides with a liner or cover of a fibrous fabric, such for example as heavy paper or cardboard, whereupon the thus prepared object is subjected to pressure suflicient to cause the expulsion of wadrate, which then sets into a stone-like mass.

stices of the fibrous fabric, by which it is absorbed, although it is also within contemplation of the invention to have-this water pass through the fibrous material and to flow away from the other side thereof. Whether it does this or not depends entirely upon the amount of water orig- This mixture, which is prefer inally added and also the pressure to which the material is subjected.

When working in accordance with the present invention, it is not necessary to maintain the pressure until the gypsum has set, because the fibrous fabric sheets protect the surface against distortion and marring, so that when the material eventually does set it will have a smooth and even surface. One of the important advantages of the process resides in the fact that pressure need be applied for only a relatively short time, as the pressure may be released in a few minutes and need not be held on the product for thirty I minutes or so or until the gypsum has hardened and set. During the pressing operation the product is not only made smooth and relatively uniform in density but also rendered sufiiciently compact so that it may be conveyed and handled with reasonable care in its unset state. As'the pressing operation causes a liberation of a considerable amount of the excess gaging water, the mass is markedly stiffened and with its paper wrapping may be subjected to considerable handling before hardening, without serious deformation.

The present invention may be adapted to the manufacture of a large variety of products which may consist of artificial lumber of various types. Thus studding and beams may be made,.which are lined on both sides, or even on all four sides, with fibrous cover sheets-for example, paper, heavy cardboard, or woven textile fabrics. The invention is equally applicable to the manufacture of relatively large flat sheets such as may be employed as wallboard, plaster board, and the like, but it is to be distinctly understood that the present invention isnot 'at all to be limited by the shape of the object produced thereby.

If desired, the plastic material may contain, in addition to the gypsum and water, suitable inorganic or organic bonding agents, or adhesives such as starch, karaya gum, dextrin, farinaceous products, prepared starch pastes, or the like. In addition thereto, fibers may or may not be used, depending upon what it is desired to manufacture. 1

The pressure employed for carrying out the present invention may vary widely, depending upon the amount and kind of fiber used, the density or other characteristics of the material desired, the type of calcined gypsum employed, the amount of water which has been mixed therewith, the characteristics of the cover sheets, and the effect of various possible additive agents. Without in any way wishing to limit the invention, it may be said that the pressure may be varied from as little as pounds per square inch to as much as 500 pounds per square inch and upward, the density of the final product depend-- ing upon the composition of the material as well as the pressure.

Let it be assumed, for example, that in accordance with the present invention it is desired to manufacture a fiat surfaced block; This may be accomplished by first placing a sheet of fabsisting of calcined gypsumfor example; ordinary stucco (calcium sulfate hemihydrate) mixed with 1% to 10% of a suitable fiber,-a small percentage of farinaceous paste, and sufficient water to produce a plastic mass. On top of this mass there is placed a second sheet of fabric, which may be similar to the first sheet or more porous or less porous, whichever it is desired to use, whereupon pressure is applied by means of a suitable pressing platen. As a result of the pressure, some of the excess water contained in the mix is forced into and through the fabric sheets, thoroughly wetting the same and, if they are thick enough, being absorbed thereby. If sufficient pressure is used, considerable water will pass through the fabric sheets, which act as filter means, and hence must be disposed of. For this purpose it is advisable to use a foraminous pressing means provided with orifices or channels through which the excess expressed water can readily escape. Such pressing means are well known in the art of pressing various iterials and hence need no detailed description 1or an understanding of the present invention. After the pressing has been carried to the desired degree, the pressure is re leased, and the block with the thereunto adhering fabric sheets is removed fromthe press and set aside to permit the setting operation to take place, after which the product is dried.

The thickness of the block is of course a matter of choice, and if the material is sufficiently thin there may eventuate a sheet that may, for example, be used as plaster board, wallboard, or the like. It is also obvious that the fabric sheets need not necessarily be perfectly smooth and flat but may be given almost any desired shape by using suitably recessed and engraved or otherwise ornamented pressing platens or pressing means, so that the manufacture of ornamental objects in accordance with the present invention is also possible and contemplated.

The process may. also be adapted for the manufacture of large sheets of wallboard, plaster board, and the like, by proceeding first to manufacture, by means already well known, a paper or cardboard lined plaster board or wallboard on a continuous plaster-board machine which turns out a continuous length of plaster board by an operation which involves the placing of a suitable core material upon an advancing sheet of cardboard or heavy paper and the superimposition thereon of a second sheet of similar paper or cardboard, whereafter the thus formed board is passed through light pressure rollers which, if desired, also serve to crimp the lower sheet about the edges to produce what is known as a folded edge board completely surrounded by paper on all four sides. If it is desired to apply the present invention to such an operation, it is advisable to press the edges of the board during the initial formation to approximately the desired size but to leave the center portion, of the board a little thicker than it is desired to have it in the final product. Immediately after this board-which is being .made on a continuous machine-has been formed it is cut by a traveling knife, and the freshly made but still unset'sheet thus produced is then subjected to pressure by means of suitable pressing means such as the platens of a hydraulic press. This pressing squeezes some of the excess water out of the core and into the fiber cover' sheets. If the pressure is sufficient, this may even cause the exudation of water from the core through the sheet, in which case the press platens must be provided with means to permit the outflow of the thus expressed water. It is of course obvious that more thanone sheet may be pressed at a time by employing a suitable multi-platen press.

It should be noted that after the pressing has been efl'ected and the core has been consolidated to the desired degree, theireshly pressed board may be removed immediately from the press and suitably supported until the gypsum core has become set and rigid. .It is not necessary to hold. the pressure on the board until the setting takes place, although obviously no harm will result if the board should set while it is still in the press, provided the water has been eliminated before setting. In any event, the board, after the gypsum core has set, is put through a suitable drier in which the moisture ,still remaining in the board is caused to evaporate. This drying must be accomplished under conditions which prevent the recalcination of the gypsum core.

In order to insure a tight but strong bond between the core and the fiber cover sheets, suit able bonding agents such as gelatinized starch, karaya gum, or other adhesives may be added to the gypsum core.

If a still stronger product is desired, a special I form of calcined gypsum having a low consistency may be employed. Thus the alpha gypsum described in Patent No. 1,901,051 may be substituted for ordinary calcined gypsum plaster. This alpha gypsum has a very low consistency, so that a a much smaller amount of water may be used in producing a slurry therefrom. It is also possibleto reduce the consistency of calcined gypsum plasters by the use of small amounts of a mixture of gum arabic and alkalis or lime, this method being applicable also to the just mentioned alpha gypsum.

It will of course be obvious that the calcium sulfate hemihydrate plasters employed in connection with the present invention may be admixed with the well known set-modifying agents, such as accelerators and retarders, so that the time of set of the material may be accurately controlled. These accelerators may consist of ground calcium sulfate dihydrate, such as set plaster or natural gypsum rock, or chemically precipitated seed crystals, or of accelerating salts, while the retarder may consist of what is known as commercial retarder," which is a. composition derived by the treatment of glue, proteins or keratinaceous material with lime,'or any other known substance that will delay the setting of the particular plaster used. These retarders and accelerators may be present in suitably balanced amounts so as to produce a definite,

predetermined setting period.

Wallboard which has been made in accordancewith the present invention is very strong and tough and far superior in strength to Wallboard which is made by merely allowing the gypsum core therein to set under ordinary conditions.

. While the invention has been described in'connection with the manufacture of Wallboard in blocks, it is obvious that other shapes can be produced, depending upon what it is desired to make. Thus studs, beams, and other architectural shapes may be made in accordance with the teachings of the present invention without departing therefrom. It is also obvious that, in addition to ordinary calcined 4 gypsum, other forms of setting gypsum' 'eements, such as Keenes cement, activated anhydrate plasters,

and the like may be substitute-d for ordinary stucco.

Obvious modifications of the present invention are to be considered within the scope therer of, for which is claimed:

1. The process of making a hard, dense and strong set gypsum Wallboard or the like which comprises gaging calcined gypsum with an excess of water over that required for the forma-' tion of calcium sulfate dihydrate, forming the 'resulting mixture into approximately the finished form of the Wallboard or the like, then compressing the product thus made by means of flat platens, atleast one of which is provided with a screen, with sufiicient pressure over substantially theentire area thereof to cause the outflow of water from the product, the pressing taking place before'the initial set of the material has taken place, removing the pressed boards from between the platens and supporting the steps of advancing a sheet of cardboard continuously in a substantially horizontal direction, placing thereon a mixture of water, calcined gypsum and fibrous fillers, spreading said mixture over the cardboard sheet, superimposing a second such sheet continuously thereon, folding the edges of one sheet over the edge of the plastic mass so as to surround the same and to form a continuously advancing wallboard having an unset gypsum core, cutting the advancing sheet into individual sheets, pressing the latter between flat platens provided with means permitting escape of expressed water. and with sufficient pressure to expel some of the excess water therefrom, removing the pressed boards thus produced, permitting them to set and harden, and drying the resulting product. v

3. The process of making dense, strong,'papercovered Wallboard which comprises placing a mixture of water, calcined gypsum, paper-fiber and a farinaceous paste on a liner of paper, superimposing thereon a similar liner, folding the edges of one liner over the other about the mixture to enclose the same, compressing the mixture at and near the edges to substantially the desired final thickness of the board and leav ing the central portion of the board somewhat thicker, and later compressing the board, be

steps of forming a board having a wet unset gypsum core and paper liners, compressing the same by means of fiat platens at least one of which is provided with a screen to permit outflow of expressed water to consolidate the core and with suiiicient pressure applied over substantially the entire-area of the board to express excess water therefrom through the paper liners, removingv the compressed board before its final set, permitting it to set and harden, and then drying the same. CARIJSLE K. ROOS. DELBER'I' F. JUR GENSEN, 'JR. 

